Heavy oil spilled on the sea as a result of shipwreck of an oil tanker etc. gets emulsified when mixed with seawater, and so acquires high degree of viscosity and remains long. If drifting ashore, the heavy oil is likely to cause enormous damage to the environment, and it takes a considerable amount of time and effort for the recovery, causing significant harm to the local economy.
Therefore, in order to minimize the damage to the environment, it is necessary to place, prior to the arrival of the spilled heavy oil at the coast, heavy oil collection equipment and oil control equipment mainly on the coast where the heavy oil is expected to drift ashore, thereby efficiently collecting the heavy oil when it drifts ashore. For that purpose, once the drifting heavy oil (floating heavy oil) is discovered, it is necessary to precisely calculate where the heavy oil will drift by running a highly precise simulation of drifting heavy oil. In order to increase the precision of the simulation, it is important to obtain a real-time location of the drifting heavy oil and oceanographic/meteorological data on the area where the heavy oil drifts, allowing the simulation to reflect such data.
As a way of discovering and monitoring a drifting substance such as drifting heavy oil and chemicals, there is a method called a fluorescence LIDAR method. When employing this method, an ultraviolet laser radar (LIDAR: Light Detection and Ranging) device is mounted on a helicopter so as to scan, from the air, the area where the substance was spilled. During this scanning, an ultraviolet pulsed laser is radiated from the laser radar device on the helicopter towards the sea surface, and the fluorescence generated at the sea surface by the radiation is photographed with respect to four different types of wavelengths by an ultrasensitive camera which is mounted on the helicopter and constituted by image intensifier tubes and a CCD camera. The information about the location of the seawater and the spilled oil is obtained from the photographed images by distinguishing between violet-blue water raman light of the seawater and blue-green fluorescence of the oil etc. It should be noted that the results of the past testing observations of spilled oil show that spilled oil whose diameter on the water surface is 15 m can be detected in the viewing field of 100 mrad when observed from 150 m in height.
This fluorescence LIDAR method, being an active system to generate fluorescence by laser excitation, makes it possible to conduct night-time observations as well as daytime observations, and to identify a spilled substance by a fluorescent spectrum. Also, because the fluorescence LIDAR method uses a CCD camera as a base for light reception, a real-time observation is possible.
However, this method causes such a problem that it is difficult to continue tracking the spill for an extended period of time because of the limited endurance of a helicopter. Therefore, the inventors of the present application have proposed a drifting substance monitoring method using an unmanned drifting substance monitoring buoy (refer to Patent Literature 1).
The unmanned drifting substance monitoring buoy in Patent Literature 1 is thrown into a water area of a drifting substance, and automatically repeats surfacing and submerging in the water area. The unmanned drifting substance monitoring buoy detects, when under the water, presence/absence of the drifting substance at the water surface and the location of the drifting substance. Thereafter, the unmanned drifting substance monitoring buoy surfaces towards the location of the drifting substance thus detected, and transmits, while afloat in the area of the drifting substance at the water surface, location information and oceanographic/meteorological data to a base station.
The unmanned drifting substance monitoring buoy surfaces or submerges by having water enter in or exit from a cylinder inside thereof. Also, when surfacing, the unmanned drifting substance monitoring buoy moves itself towards the location of the detected drifting substance by adjusting its moveable wings. That is, the movement of the unmanned drifting substance monitoring buoy towards the drifting substance is made by a surfacing force, and a direction of the movement is decided only by adjusting the moveable wings. Therefore, the unmanned drifting substance monitoring buoy reduces energy consumption for tracking the drifting substance, and makes it possible to track the drifting substance for an extended period of time (from several days to several weeks), compared to the case of utilizing a propulsion device such as a propeller for tracking a drifting substance.